The present invention relates to an etchant, a method of manufacturing a substrate for electronic device by using an etchant, and an electronic device having the substrate, and especially an etchant in which each layer of wiring formed by stacking an Al layer, or Al alloy layer, and a Ti layer, or Ti alloy layer, can be uniformly etched to a substantially equal etching rate by the etchant.
Al as a wiring material has an advantage of having low resistance, and it is frequently used as the wiring material of an electrode etc. on a substrate of an electronic device.
As an example of the electronic device, FIG. 12 is a plan view showing a thin film transistor in a conventional thin film transistor LCD.
The thin film transistor 82 comprises a gate electrode 84 formed on a substrate 83 and a gate insulating layer 85 to cover the gate electrode 84. A semiconductor active layer 86 of an amorphous silicon (hereinafter, “a-Si”) is formed on the gate insulating layer 85 of the upper gate electrode 84. And a source electrode 88 and a drain electrode 89 are extended on the gate insulating layer 85 or semiconductor active layer 86 wherein ohmic contact layer 87 composed of amorphous silicon having n-type impurity like phosphorus(P) (hereinafter, “n+ a-Si”) is inserted. Also a passivation layer 90 covering a thin film transistor 82 made up of the source electrode 88, the drain electrode 89, and the gate electrode 84 is formed, and a contact hole 91 is formed on the passivation layer 90 of the drain electrode 89. Further a pixel electrode 92 constituted by a transparent electrode layer of indium tin oxide (hereinafter, “ITO”) electrically connected with the drain electrode 89 through the contact hole 91 is formed.
And the left part of FIG. 12 shows a sectional view of a gate terminal pad 93 of the gate wiring. A contact hole 95 passing through a gate insulating layer 85 and a passivation layer 90 is formed on the lower pad layer 94 composed of gate wiring material on the substrate 83, and a upper pad layer 96 constituted by a transparent electrode layer is electrically connected with a lower pad layer 94 through the contact hole 95. Also a source wiring is of similar structure to the gate wiring.
As mentioned hereto, for example, in the thin film transistor, the transparent electrode layer constituting a gate terminal, a source terminal and a pixel electrode is directly connected with a metal for wiring constituting the gate wiring, the source wiring and the drain electrode.
By the way, in the case of using the Al metal layer as a wiring material in order to reduce the wiring resistance in the electronic device, a hillock is generated. The hillock is generated as a needle-shaped projection on the surface of the Al layer during a heat treatment. The projection is passed through the stacked insulating layer so that a short circuit is generated with another conducting layer, or a poor insulation occurs. Also if the ITO were directly contacted with the Al, oxygen of the ITO should oxidize the Al, as a result, the electric resistance of contact part should be increased.
In order to prevent the above problem, a stacked layer, produced by forming another metal layer like Mo layer or Cr layer on the Al layer (hereinafter, “different metal stacked layer”), has been widely used. In the case of providing a gate electrode 84 in a stacked layer of the different metal from each other, for example, as shown in FIG. 14A, a photomask 97 of a desired pattern is formed on the surface of stacked layer 84c stacking an Mo layer 84b on the Al layer 84a formed on the substrate 83 by photolithography. And then, the stacked layer 84c is obtained from uniform etching by using an etchant having H3PO4 of 80 wt %, HNO3, CH3COOH and H2O.
By the way, in the case that it is patterned by uniform etching of the different metal stacked layer, a battery reaction of the etchant is generated by the potential difference between the metal layers, and an under-cut is generated, in which a line width of the Al layer 84a in the lower layer is shorter than a line width of the Mo layer 84b in the upper layer as shown in FIG. 14B, because the Al layer in the lower layer is more quickly etched than the Mo layer in the upper layer. Also a problem of poor insulation enduring press may be generated.
Therefore, in order to solve these problems, after the uniform etching, sunscreen-shaped Mo layer 84b can be patterned by added etching by using an uric acid.